1. Field of the Invention
This invention relates to a method and an apparatus for the downward transfer of concrete, which method and apparatus are particularly suitable for placing concrete or mortar across a high head at an angle relative to a vertical.
2. Description of the Prior Art
It is often necessary to downwardly transfer concrete vertically or with an inclination to the vertical in constructing various structures, such as vertical or inclined shafts of tunnels, underground power plants, vertical or inclined surfaces of building foundations, and dams. The recent trend is to build large structures deep in the ground, and the head and inclination for the downward transfer of concrete are increasing.
Heretofore, to downwardly transfer concrete through a path with or without an inclination, buckets, chutes, and concrete pumps are used depending on the scale and site conditions of the construction. A typical bucket system of the prior art is a concrete conveyor having a bucket driven by a winch, in which the bucket has wheels so as to move up and down along rails mounted on the inclined surface or in the shaft. The concrete pumps of the prior art are suitable only for the cases with a small angle relative to a horizontal.
The concrete downwardly transfered by buckets has shortcomings in that a continuous supply of the concrete is impossible and that if the head is high the vertical travel of the buckets takes time, so that efficiency of the work is low. Besides, when a worker is stationed at the place where concrete is deposited by the bucket, he is exposed to the risk of being hit by concrete particles or blocks which separate from the bucket moving above him and drop downward.
Open chutes and steel pipe chutes have been used for downwardly transfer of concrete. Such chutes, however, have shortcomings in that aggregates and mortar ingredients of the concrete tend to be separated as the concrete moves downward and that, when the head is high and the inclination relative to a horizontal is large, the velocity of the concrete at the outlet end of the chute becomes so high that a considerably large impact is applied to the place where the concrete drops and the high speed collision of the concrete there tends to increase the separation of the concrete ingredients, causing adverse effects on the quality of the concrete placed, on protection of reinforcing steel members and members to be buried at the place of concrete placing, and on the safety of the workers.